There have many studies on how listening to or playing the music of Bach affects the brain. One of the most interesting stories on some of this research was recounted on PBS’ Nova series in 2009.
The story, entitled A Mind for Music, chronicles the late neuroscientist and writer, Oliver Sacks as he undergoes a series of MRI scans to learn more about how his brain responds to music and, particularly, the music of J.S. Bach. The results are fascinating. Read and listen to the story here.